Before you begin

Application Default Credentials

Client libraries can use Application Default Credentials to easily
authenticate with Google APIs and send requests to those APIs. With
Application Default Credentials, you can test your application locally and
deploy it without changing the underlying code. For more information,
including code samples, see Google Cloud
Platform Auth Guide.

When you create a service object with the BigQuery Client
Libraries and do not pass in explicit
credentials, your application will authenticate using Application Default
Credentials.